In mobile telecommunication systems, there always exists frequency offset in a signal transmitted from a radio transmitter to a radio receiver. The frequency offset may be caused by a frequency difference between oscillators of the transmitter and the receiver, but a major cause for the frequency offset is Doppler shift affecting the signal in a mobile environment. The Doppler shift is caused by the change in the distance between a mobile terminal and a base station due to the movement of the mobile terminal.
Frequency offsets typically leak to a baseband part of the receiver, thereby causing a phase rotation, i.e. frequency error, in a received baseband signal. This phase rotation has to be compensated for in order to ensure a reliable detection of received data. First of all, the frequency error introduced into the received signal is estimated and, thereafter, the phase rotation in the received baseband signal is compensated for by weighting the received signal with estimated phase rotation values which are used for rotating the phase of the received signal into the opposite direction.